I've just enabled profile avatars for us, here -- at least for the moment. They're still totally optional, but they're fun. I uploaded a 14K animated .GIF for myself as a test, and it works a treat. (However, if the tick-tock-tail kitty is too distracting or whatever, I'm happy to change it. As I said, this is a test; we'll see how it goes.)

I don't see anything that has been published for Gravatar support in phpBB3. I see one hack for phpBB2.0.4 - 2.0.11 tough. Don't know for sure if it would work and it'd involve manual editing of a few of the board files.